Gas lift valve



M. B. THOMAS GAS LIFTVALVE Oct. 8, 1940.

F'-ed Feb. 18, 1938 3 Sheta-Sheet 1 FIQE;

r FIGA;

INVENTOR.

" ATTORNEY.

Oct. 8, 1940. M. e. THoMA (AS LIFT VALVE Filed Feb. 18. 1933 3 Sheots-She et 3 m I I x 5 6 7 3 14775 3 1 Z///// 4 `K HA i 4 i I I 85 l /f// A f 2 V 9 ATTORNEY- patente& Oct. 8, 1940 UNITED sTrEs 'PATENT OFFICE 11 Claims.

The present invention is directed to gas lift valves for use in the propulsion of liqud from a low level to a higher level. Primarily, it is concerned with gas-lift valves to be used in oil wells.

As is known, a deposit of petroleum oil is usual`- ly accompanied by a gas deposit which presses down on the upper surface of the oil and assists in forcing it to the surface. Inevitably, the oil produced contains more or less dissolved or suspended gas whereby in flowing' through tubing from the deposit to the surface its apparent specific gravity is less than its actual specific gravity.

It has been the practice to rely on this decrease of density of oil by aeration or gasification to increase the flow of oil in wells in which the formation pressure has become too low for normal flow. The aeration' has been accomplished by providing valves along the tubing and forcing gas, by one means or another, through these valves into the oil in the tubing thereby imparting a decrease in apparent specific gravity and a lifting action to it. i

Hitherto, these valves have operated either on the pressure differential principle, according to which the head of oil in the tubing is directly opposed to a. gas pressure outside the tubing, or vice Versa, or the velocity principle, according to which the valve will open when the velocity of the oil drops below a certain predetermined minimum. Both types have the disadvantage that shouldthe oil in the tubing or.casing, as the case may be, drop below the level of any of the valves, these valves will open thereby leading to a waste of gas and an actual repression of oil flow. In addition, when a string of such valves is employed, as is usually the case, more valves than are actually needed are generally set into operation, thereby causing an expensive waste of gas.

The primary object of the present invention is the provision of a valve'of this general type which operates on a principle quite different from those previously relied upon, this principle being that when the flowof oil in a tubing or casing, as the case may be, decreases or stops, the apparent specific gravity of the oil increases due to the loss or reduction of gas therein. The valve of the present invention depends for operation -on this change in gravity.

A further object of the present invention is the provision of a valve which so operates that when a string of them is .employed no more than are actually required will operate to feed gas into the oil.

(Cl. 103-232) i An additional object. of the present invention is the provision of a valve of the type described which is simple in construction and has a minimum of moving parts, whereby initial cost and maintenance are reduced. 5

Further objects and advantages of the present invention will appear from the following detailed description of the accompanying drawings, in which- Figure 1 is a side-elevation, partly insection, 10 of a valve arrangement according to the present invention;

Figure 2 'is a front elevation of the arrangement shown in Figure 1;

Figure 3 is a side elevation, partly in section, 15 of a modification of the arrangement shown in Figure 1;

Figure 4 is a side elevation, partly in section, of another modification of the arrangement shown in Figure 1; and p 20 .Figure 5 is a side elevation, partly in section, of still another modification of the arrangement shown in Figure l. A

Referring to Figure 1 in detail, the valve mechanisIn-is assembled on the outside of a tubular 25 member I which will correspond in diameter to ,the tubing used in the well and which is provided with 'a coupling 2 on one end and has its other end screw threaded for connection in a string of tubing. This tubing is surrounded in a well 30 by a casing 30 which is of larger diameter. Thus the valve mechansm is arranged in the annular space between the tubingand the casing.

As previously stated, the valve of the present invention operates on the difierence in specific 35 gravity of the liquid being produced and a standard liquid. To this end a casing 3 is attached, by welding or otherwise, to the wall of the tubing and is provided with two interior chambers 4 and 5 separated by a diaphragm 6 in the center of 40 which is a screw threaded nut 'I in which is mounted a stud B which terminates as a valve head 9 adapted to cover port lil, which, when open. connects the space betweenthe casing and the tubing with the interior the latter through 45 tube ll.

Chamber 5 is connected to'the interior of tubing l by a short pipe |2 which enters tubng l at apoint designated as A. Chamber 4 is connected to the interior of tubing l through a riser 50 |3 which enters tubing I at a point designated as B 'which may be any selected distance t'i-om A and will usually be at' least ten feet above A. The upper 'end of riser l3 actually terminates in the upper end of chainber I' l which is mounted on 55 the side of the tube. A short length of tubing connects'the lower end of chamber l4 to the interior of tubing I. A plug [6 is provided in the upper end of chamber |4 so that the chamber and the riser 'and chamber 4 may be filled with the standard liquid. The arrangement ofriser I3 and tubing |5 in chamber I 4, serves to' prevent the standard liquid from becoming contaminated by the liquid inside tubing l. Riser |3 is provided with a choke ll, to prevent chattering of valve head 9.

The pipe I l connects with the interior of tubing I at a point C above point B. The reason for this arrangement is that since the gas lift valve is operated by a difierence in specific gravity of the liquid in tubing I between points A and B, and the liquid in the riser tube between the same points, its operation would become undesirably intermittent if the gas admitted by it were to enter the column of liquid in the tube between points A and B. In other words, by the arrangement shown the shutting-ofi of the chamber by its -own operation is -.avoided. Pipe ll is provided with a standard check valve !8, which may be omitted if desired.

The operation of the above described arrangement is relatively simple. The chamber 4 and the riser |3 and chamber l4 arefilled with a liquid' which has a specific gravity intermediate that of the oil being produced when it is free of gas and when it contains enough gas to flow readily under ormation pressure, and preferably as close as possible to the latter; that is, the liquid in the riser should have a specific gravity approximating the specific gravity of the oil when it is actually flowing. In other words, this liquid will have a lower specific gravity than would the oil produced after it has been freed from gas.

Let it be assumed that oil is flowing in tubing I. In this case, the column of liquid in the tubing l between A and B will be lighter per um't area than the column of liquid in the riser between the same points, whereby the pressure in chamber 4 willbe greater than that in chamber 5 and valve head 9 will be seated on inlet port o. Even when thegravity of the liquid in the riser is the 'same as that of the flowing oil the valve will still remain seated. If for some reason the oil flow in tubing I should' stop, the gravity of the liquid between points A and B will gradually in'- crease due to gas loss until this column becomes heavier per unit area than the column of liquid inthe riser, whereupon the pressure of chamber 5 will tend to exceed that in chamber 4 and push valve'head 9 off inlet port o, allowing high pressure gas from the casing to pass through pipe ll into the tubing I at point C, thereby lifting the liquid above this point up through the tubing. Valve 9 will remain open until, by reason of the operation of a lower situated valve; the weight oi the liquid in tubing l between points A and B again becomes less, or not more, per unit area than the weight of the liquid in the riser.

The operation of a set of the above described` the open position and admit fluid from the casing into the tubing, unloading any liquid in the tubing above this valve. Fluid will continue to pass through this valve from the casing into the tubing until the liquid level in the casing has been pushed far enough down to uncover the next lower valve.

If the fluid inside the tubing opposite the second valve is dead and has not been aerated by gas from the producing formation sufiiciently to lower its specific gravity below that of the fluid in the riser tube, the valve will be in open position and admit fluid from the`casing into the inside of the'tubing. This gaseous fluid will' rise inside the tubing and lighten the fluid opposite the valve above sufliciently to close it. Fluid will continue to enter the tubing from the casing through the second valve until the liquid level in the casing has been pushed down far enough to uncover the next lower or third valve and admit gaseous fluid at this point. r

In like manner, the valves in the tubin string below this point will be uncovered successively as the liquid level in the casing is lowered by the gaseous fluid injected into the casing, closing the next higher valve as the valve underneath admits gaseous fluid into the tubing string, until a point will be reached where the available input fluid pressure on the casing will push the liquid level in the casing down no farther, at which point gaseous fluid will continue to pass from the casing into the tubing through the lowest valve above the liquid level in the casing that has a greater pressure outside the tubing than inside, all valves above this valve remaining closed.

Should the casing pressure at the surface decrease sumciently to permit the liquid level in the casing to rise above the valve where gaseous fluid is being admitted into the tubing, then the admission of gaseous fluid into the tubing will be cut off and flow up the tubing string might then stop for want of gas to sufliciently aerate fluid in the tubing and permit dead fluid to settle baclE down the inside of the tubing. When this dead fluid inside the tubing rises to the first valve above the liquid level in the casing, the specific gravity of the fluid in the tubing will then be great enough to open this valve and admit gas from the casing into' the tubing and resume flow out of the well. The valves will react in a similar manner to slugs of fluid being pushed up the tubing, and will open and admit gaseous fluid into the tubing as long as a slug of dead fluid of the length equal to the spacing between the two diaphragm tubes inside the tubing is opposite any valve.

The arrangement shown in Figure 3 dffers from that shown in Figure 1 in that it is adapted for an operation in which oil is produced by being caused to flow upwardly between the tubing and the casing and high pressure gas is fed in through the tubing. For this reason, pipes |2 and !5 open to the exterior of tubing I instead of to its interlor. This is also true of tube I I. Inlet port ID, on the other hand, is connected to the interior of tubing l by an additional tube !9.

The arrangement shown in Figure 4 diflers from that shown in Figure 1 only in that the valve assembly is aflixed to the interior of the tubing I instead of to its exterior. To this' end the plug which carries the inlet port o is extended through the wall of tubing I so as to communicate with the space between the 'tube and the casing. Likewise, since plug !6 must be accessible outside the tubing, a pipe 20 is connected to the opening at the top of chamber M and to the wall of tubing l and plug 16 is inserted into the end of this pipe.

The arrangement shown in Figure is used for wells in which the flow of oil is upwardly between the tubing and the casing. In order to provide for this, tube ll is extended to the wall of the tube l and communicates with the exterior thereof. Likewise, pipes l2 and !5, instead of terminating inside of tubing l, are extended to the wall of tubing l and communicate with the exterior thereof. otherwise the arrangement is precisely thesame as that illustrated in Figure 4.

The above discussion has been based on an assembly in which the valve 9 is on its seat when the' diaphragm is in neutral position and the liquid in the riser has a gravity less than that of the oil produced from the well when it is free of gas. It is apparent that the combination of parts will function similarly when valve 9 is of such length as to be off its seat when the dia-` phragm is in neutral position and a liquid having the same gravity as the oil produced when it isfree of gas is employed in the riser. In many cases this arrangement will be more convenient since it permits the use of dead oil produced from the deposit in the riser. With this oil in the riser the length of the valve and the strength of the diaphragm can be so adjusted that the valve will remain open until the liquid in the conduit being produced from the deposit has a gravity which may, for example, be at least 25% less than the gravity of the dead oil. consequently, when the oil in the conduit contains enough gas to flow, the valve will be closed by reason of the greater gravity of the dead oil in the riser. As flow in the conduit diminishes and the gravity of the oil in the conduit increases by reason of loss of gas, and approaches the gravity of the dead oil in the riser, the valve will open and start the injection of gas into the conduit.

This latter arrangement has the distinct advantage tha-t it makes possible the maintenance of the lowest exposed valve on the string of tubing in open position.. The gravity of the fluid being produced from the deposit increases with depth. consequently, the deeper in the well the valve is placed, the closer will the fluid in the conduit approach the dead oil in the riser in gravity and the greater will the tendency of the valve to remain open become.

Various changes in the above described arrangements may occur to those skilled in the art. For example, the sensitivity of the valve assembly may be increased by increasing the height of the riser and/or increasing the size of the dia-phragm.

Positive action of the valve may be aided by the arrangement of suitably selected springs on either or both sides of the diaphragm or around the valve stern. The particular type of valve illustrated, which was designedly chosen simply for ease of description, may be replaced by any one of the number of known valves of different design All such changes in arrangement of parts and size and design of individual elements which do not involve a departure from the basic principles underlying the present invention are contemplated within the scope of the appended claims in which it is intended to claim the invention as broadly as the prior art permits.

I claim:

1. An assembly for the production of fluid from a subsurface' deposit comprising a conduit establishing fluid connection between said deposit and the surface, a source of high pressure gas, a passage connecting said source to the interior of said conduit, a valve for controlling said passage, and means sensitive only to the gravity of the fluid in said conduit below the point of connection thereto of said gas passage for-fixing the position of said valve.

2. An assembly for the production of oil from a subsurface deposit comprising a conduit establishing fluid connection between said deposit and the surface, a diaphragm arrang-ed adjacent the wall of said conduit, a source of high pressure gas, a passage connecting said source to the interior of said conduit, a valve for controlling said passage actuated by said diaphragm, a chamber on each side of said diaphragm, means connecting one of said chambers to the interior of said conduit, means for maintaining a constant head of a liquid of selected gravity connected to the other chamber and means connecting the top of said head of liquid to the interior of said conduit.

3. In an assembly for producing oil from a subsurface formation, in combination, a conduit for leading the oil from the formation to the surface, a source of high pressure gas normally maintained out of fluid connection with said conduit by a valve, means adjacent the wall of said conduit for holding a column of liquid of selected specific gravity, means for' opposing said column to a column of liquid of the same height in the conduit, and means actuated by a difference in specific gravity between the liquids of said columns for controlling the position of the aforesaid valve.

4. In an assembly for producing oil from a sub-- surface formation, in combination, a conduit for leading the oil from the formation to the surface, a source of high pressure gas normally maintained out of fluid connection wtih said 'conduit by a valve, means adjacent the wall of said conduit for holding a column of liquid of selected specific gravity, means for opposing said column to a column of liquid of the same height in the conduit, and means actuated by a difference in specific gravity between the liquids of said columns in favor of the liquid of selected specific gravity for opening the aforesaid valve.

5. A flow valve of the character described having its Component parts mounted adjacent the wall of a conduit connecting a subsurface formation with the surface comprising a pair of chambers separated by a partition, a diaphragm in one chamber dividing it into two sections, a fluid inlet passage and a fluid outlet passage arranged in the other chamber, a, tube connecting said and a, valve for controlling said inlet passage having its stem passing through sa'id partition and attached to said diaphragm and means for actuating said diaphragm.

6. In an assembly for producing oil from a subsurface formation, in combination, a conduit for leading the oil from the formation to the surface, a source of high pressure gas, a pair of juxta- "posed chambers separated by a' partition arthe aforesaid given point, a fluid connection bea twen the second chamber and the interior of fluid outlet passage to the interior of said conduit g said. conduit at a point above the point of connection of the riser thereto, a fluid connection between said second chamberand the source of high pressure gas, and a valve actuated by said diaphragm for controlling the last mentioned fluid connection.

'7. A combination, according to the preceding claim, in which the riser terminates in the upper end of a chamber the lower end of which is in fluid connection with the interior of the conduit.

8. In an assembly for producing oil from a subsurface formatiomin combination, a conduit for leading the oil from the formation to the surface, a source of high pressure gas', a passage connecting said source to the interior of said conduit at a selected point, a valve for controlling said passage, means adjacent the Wall of said conduit for holding a column of liquid of selected specic gravity, means for oppQsing said column to a column of liquid of selected height in said conduit, said latter column being below the point of connection of said high pressure gas passage to said conduit, and means actuated by changes in specific gravity in said column of conduit liquid for controlling the position of the aforesaid valve.

9. An assembly for producing oil from a subsurface formation comprising a conduit for carrying oil from the formation to the surface, means for introducing gas under pressure at a point in said conduit, and means for regulating the flow of gas into the conduit solely in response to variations in the gravity of the oil in a relatively short section in said conduit.

10. A gas lift apparatus for oil wells comprising a conduit for carrying oil from the producing formatio'n to the surface, means for ntroducing gas under pressure at a selected point in said conduit, and means responsive to variations in the gravity of oil in said conduit at a point below said point of introduction of gas for regulating the flow of gas into the conduit.

11. Apparatus for maintaining a constant gas oil ratio in afiuid eduction pipe in a gas lift well including means for opposing a head of liquid of selected gravity against a corresponding head of oil in said pipe, means for supplying gas into the induction pipe, and means for varying the supply of gas into said pipe in proporton to variations in gravity in said selected head of oil in said pipe.

MAURICE B. THOMAS. 

